Dual field of view optics with non-mechanical switching

Abstract

An all-refractive optical system that images a scene at two different fields of view or FOVs, with switching between FOVs enabled by switchable lens elements is disclosed. The two fields of view vary in focal length by a factor of three. The wide FOV images broad-band Short Wave InfraRed SWIR radiation at an f/number of 1.7, while the narrow FOV images narrow-band illuminated SWIR at f/4.9. A voltage change across the switchable lens elements generates an optical power change between finite focus and infinite focus. Situated among static optical elements, the switching elements enable FOV changes with no mechanical movement. The given f/numbers at each FOV are a result of a fixed aperture in the system. The smaller throughput in the narrow FOV mode is augmented by narrow-band illumination of the scene to maintain equivalent sensor response between the two FOVs.

What is claimed is: 
     
       1. A compact optical imager that can switch field of view without mechanical motion, comprising:
 a first electrically switchable lens capable of receiving either wide broadband or narrow spectral band rays on its front aperture; 
 a meniscus lens with its front aperture facing a back aperture of the electrically switchable lens; 
 a negative lens with its front aperture facing a back aperture of the meniscus lens; 
 a positive lens with its front aperture facing a back aperture of the negative lens; 
 a second electrically switchable lens configured to face a back aperture of the positive lens; and 
 an SWIR focal plane array configured to receive a focused image from the second electrically switchable lens. 
 
     
     
       2. The compact optical imager according to  claim 1 , wherein the meniscus lens is based on ZnS, the front aperture of the meniscus lens having an aperture diameter of 33 mm and a radius of curvature 37.33 mm, and the back aperture having an aperture diameter of 29 mm and a radius of curvature of 112.85 mm. 
     
     
       3. The compact optical imager according to  claim 1 , wherein the negative lens is based on AMTIR-1, the front aperture of the negative lens having an aperture diameter of 17 mm and a radius of curvature of −56.55 mm, the back aperture having an aperture diameter of 20 mm and ROC of 33.23 mm. 
     
     
       4. The compact optical imager according to  claim 1 , wherein the positive lens is based on ZnSe, the front aperture of the positive lens  4  having an aperture diameter of 30 mm and a radius of curvature of 67.46 mm, its back aperture having an aperture diameter of 30 mm and a radius of curvature of −58.07 mm. 
     
     
       5. The compact optical imager according to  claim 1 , wherein a front aperture of the second electrically switchable lens faces the back aperture of the positive lens, both the front and back aperture diameters of the second electrically switchable lens being 25.4 mm. 
     
     
       6. The compact optical imager according to  claim 1 , wherein for broad-band SWIR radiation of 1.0-1.7 μm, both the first and the second electrically switchable lenses are electrically set in an infinite focus state to resolve a wide FOV image onto the SWIR focal plane array. 
     
     
       7. The compact optical imager according to  claim 1 , wherein for a narrow spectral band radiation centered around 1.54-1.56 μm, the first electrically switchable lens is set to a state of positive-focus, and the second electrically switchable lens is set to a state of negative-focus, to focus a narrow FOV image onto the SWIR focal plane array. 
     
     
       8. The compact optical imager according to  claim 7 , wherein active illumination of a scene boosts total light energy collected at the focal plane array. 
     
     
       9. The compact optical imager according to  claim 1 , wherein finite focus and infinite focus electrically switchable states of the first and second electrically switchable lenses are used to alter an effective focal length of the compact optical imager such that wide FOV images broad-band short wave infrared radiation at an f/number of 1.7, while the narrow FOV images narrow-band illuminated short wave infrared radiation at f/4.9. 
     
     
       10. A compact two field of view imager which uses switchable lenses to generate two different effective focal lengths for the system, comprising:
 a first electrically switchable lens capable of receiving either wide broadband or narrow spectral band rays on its front aperture; 
 a ceramic lens with its front surface having a conic term and a 10th order even asphere facing a back aperture of the electrically switchable lens as an aperture stop; 
 a first glass lens with its front spherical surface facing a spherical back surface of the ceramic lens; 
 a second glass lens with its front surface having a conic and a 10th order even asphere facing a spherical back surface of the first glass lens; 
 a second electrically switchable lens configured to face a spherical back surface of the second glass lens; and 
 an SWIR focal plane array configured to receive a focused image from the second electrically switchable lens. 
 
     
     
       11. The compact two field of view imager according to  claim 10 , wherein the ceramic lens is based on a miltran ceramic, its front aperture having an aperture diameter of 33 mm and a radius of curvature 35.82 mm, and its back aperture having an aperture diameter of 29 mm and a radius of curvature of 141.22 mm. 
     
     
       12. The compact two field of view imager according to  claim 10 , wherein the first glass lens is based on NRL  4  glass, its front aperture having an aperture diameter of 22 mm and a radius of curvature of 78.65 mm, its back aperture having an aperture diameter of 19 mm and ROC of 20.84 mm. 
     
     
       13. The compact two field of view imager according to  claim 10 , wherein the second glass lens is based on NRL  7  glass, its front aperture having an aperture diameter of 29 mm and a radius of curvature of 97.31 mm, its back aperture having an aperture diameter of 29 mm and a radius of curvature of −74.69 mm. 
     
     
       14. The compact two field of view imager according to  claim 10 , wherein a front aperture of the second electrically switchable lens faces the back aperture of the second glass lens, both the front and back aperture diameters of the first electrically switchable lens being 38.1 mm, and both the front and back aperture diameters of the second electrical switchable lens being 25.4 mm. 
     
     
       15. The compact two field of view imager according to  claim 10 , wherein for broad-band SWIR radiation of 1.0-1.7 μm, both the first and the second electrically switchable lenses are electrically set in an infinite focus state to resolve a wide FOV image onto the SWIR focal plane array. 
     
     
       16. The compact two field of view imager according to  claim 10 , wherein for a narrow spectral band radiation centered around 1.54-1.56 μm, the first electrically switchable lens is set to a state of positive-focus, and the second electrically switchable lens is set to a state of negative-focus, to focus a narrow FOV image onto the SWIR focal plane array. 
     
     
       17. The compact two field of view imager according to  claim 16 , wherein active illumination of a scene boosts total light energy collected at the focal plane array. 
     
     
       18. The compact two field of view imager according to  claim 10 , wherein finite focus and infinite focus electrically switchable states of the first and second electrically switchable lenses are used to alter an effective focal length of the compact two field of view imager such that two different f/numbers and FOVs are achievable.